The neurophysiological basis of bladder inhibition in response to intravaginal electrical stimulation

Intravaginal electrical stimulation (IVS) induces a profound bladder inhibition and is successful in the treatment of incontinence due to detrusor instability. In this experimental study in cats, direct recordings of the efferent activity in thin hypogastric and pelvic nerve filaments to the bladder were used to analyze the neuronal mechanisms underlying this bladder inhibition. A longlasting reflex discharge, with a latency of 35 to 50 msec., was evoked in the hypogastric nerve by IVS. The reflex discharge was unaffected by imposed changes in intravesical pressure or by micturition contractions, but the response was very frequency-sensitive with an optimal transmission at about 5 Hz of stimulation. A "spontaneous" efferent activity could be recorded in the pelvic nerve filaments when the bladder pressure was elevated above 5 to 7 cm. H2O. The pelvic activity occurred in 10 to 20-second bursts, each followed by an abortive detrusor contraction. IVS of 5 to 10 Hz completely abolished this efferent pelvic activity by central inhibition. The findings are discussed in relation to the normal neuronal control of the bladder and to the clinical application of IVS.